Grafet: The Sequential Function Chart

Sequential function chart (SFC) is a graphical programming language used for programmable logic controllers (PLCs). It is one of the languages defined by IEC 61131-3 standard.It can be used to program processes that can be split into steps.


During 1975, fourty French speaking researchers and industrial managers, involved in complex discrete system control, used to meet every two months to compare and investigate models and methods for building sequential system control. After two years of hard and laborious meetings, talks, chats and studies, they proposed a model called GRAFCET. This name came from "graph" because the model had a graphic basis, and AFCET (Association française de cybernétique économique et technique) from the scientific association which supported the work. The basic concepts of this discrete system model where, and remains today, quite clear and simple

Main Components


This model mixed the ability of the Petri net model, for concurrent modelling, the softness of the boolean function, to represent complex decision functions, and included directly delayed signal definition. All the features were judged necessary to suit real industry requirements. The dynamic behaviour was first written as five evolution rules: